This high top sneaker is part of the Mou-te B campaign promoted by the Barcelona City Council to encourage the use of public transport, bicycle, or walking through the city. There are other similar campaigns that combine Catalan word Bé and B from Barcelona, like Fem-ho B (let´s do it right) or Recicla B (recycle well). My free translation for Mou-te B would be "move properly".
The big tennis shoe was first seen at Plaça Universitat and it was supposed to be kept somewhere safe during weekends. Now it seems to stay for good next to Picornell Olympic swimming pools where it is succumbing little by little to vandalism. Hurry up, you don´t have much time to take your picture.
See Mou-te B sneaker Picture on a Google Earth Map